Shockproof brush holder assembly



y 8, 1962 H. 0. SHORT 3,034,006

SHOCKPROOF BRUSH HOLDER ASSEMBLY Filed March 2, 1959 2 Sheets-Sheet lINVENTOR. HAROLD 0. SHORT May 8, 1962 Filed March 2, 1959 H. 0. SHORTSHOCKPROOF BRUSH HOLDER ASSEMBLY FlG-3 2 Sheets-Sheet 2 INVENTOR. HAROLD0- SHORT United States Patent 3,034,006 SHOCKPROOF BRUS HOLDER ASSEMBLYHarold 0. fihort, Towson, Mi, assignor to The Black and DeckerManufacturing Company, Towson, Md, a corporation of Maryland Filed Mar.2, 1959, Ser. No. 796,430 2 Claims. (Cl. 310247) The present inventionrelates to a brush holder assembly for an electric motor, and moreparticularly, to a shockproof brush holder assembly capable ofwithstanding extreme environments of shock and vibration.

The present invention will be described with refer ence to an electrictool of the percussive type; but it is to be understood that theessenceof the present invention is not to be limited thereby, but is tobe adaptable to any application wherein the brush holder assemblies aresubjected to extreme and unusual conditions of impact shock, vibrations,and various mechanical forces.

In a high-capacity portable electric hammer, for example, of the typecapable of drilling a two inch cylindrical hole in solid concrete fourinches deep in one minute, the shock and mechanical recoil forcesoperating upon the tool are necessarily tremendous; and the result issuch that the tool is self-destructive and breaks down after continuoususage of approximately 50 hours. A habitual cause of tool failure arethe brush holder assemblies for the electric motor, which heretofore,had to be replaced or repaired in about every 50 hours. For example, thebrush cap (no matter how tightly threaded) would soon become loosened,or the brush spring would soon buckle and thus fail to force the brushfirmly against the motor commutator, or in general, the various partswould soon become loose and quickly disengage. The relative movementbetween the loose parts would rapidly precipitate an early failure, orquite often, the entire brush holder assembly would simply pop out ofthe motor casing.

Accordingly, it is the general object of the present invention toprovide a rugged, reliable brush holder assembly capable of withstandingextreme shocks and vibra- 3,034,906 Patented May 8, 1962 inder islightly press-fitted into the motor casing to allow the protruding brushto make sliding contact with the motor armature in the conventionalmanner. A suitable roll-pin is lodged between the outer cylinder and themotor casing, transversely to the axis of the cylinder, so as to lockthe cylinder within the casing; and an outer continuous steel band issecured directly to the motor casing and is positioned over thecylinders to preclude their escape from the motor casing. Means are thenprovided to make a suitable electric contact with the protruding lowerportion of the inner conducting cylinder.

The present invention will become more apparent from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIGURE 1 is an exploded view of the brush holder assembly, showing inpictorial view all of the parts, with tions and yet render fullperformance for at least 500 hours.

It is a specific object of the present invention to provide a simple,but rugged, brush holder assembly capable of being manufactured easilyand economically.

In accordance with the teachings of the present invention, twoconcentric hollow cylinders are nested and firm- 1y press-fitted withineach other in such a manner whereby the inner cylinder is recessed belowand protrudes below the outer cylinder. The inner cylinder is made of aconductive material, such as brass, and functions as a brush holderinsert; while the outer cylinder is made of a suitable insulationmaterial, such as fibre, and acts as an insulated outer sleeve. Thelower portion of the inner conducting cylinder has an axial rectangularslot machined therein so as to snugly and slidably house a rectangularcarbon brush which protrudes therefrom; while the upper portion of theinner conducting cylinder has an axial counterbore, which communicateswith the axial rectangular slot and which is internally-threaded. Eachcylinder has a suitable cap secured thereto, and each cap is providedwith external threads adapted to engage the internal threads of therespective cylinders. The cap for the inner cylinder is known as thebrush cap, and it is made of a suitable conducting material. Lock washermeans are provided to hold the brush cap securely in place. The brushcap is provided with a blind axial bore, which is adapted to fully guidethe conventional brush spring and shunt. The cap for the outer cylinderis made of a suitable insulating material, such as hard fibre, andengages the inner threads of the outer cylinder. The outer cyltheexception of the outer steel band;

FIGURE 2' is a view of the type of electric tool in which the presentinvention is used; and

FIGURE 3 is a view taken at line 33' of FIGURE 2.

With reference to FIGURES l and 3, an insulated outer sleeve 1 (in theform of a hollow cylinder) has counterbored portion 2 that is providedwith suitable internal threads 3. Outer sleeve 1 is made of a suitableinsulation, such as hard fibre. A brush holder insert 4, made of brassor other suitably conducting material, is likewise made in the generalform of a hollow cylinder. Brush holder insert 4 is adapted to be nestedand firmly pressfitted within outer sleeve 1 in such a manner wherebybrush holder insert 4 is recessed below and protrudes below outer sleeve1, as shown more particularly in FIG- URE 3. Other means of securingbrush holder insert 4 within outer sleeve 1 may also be used, but atight press-fit is recommended for ease and economy of manufacture. Anaxial rectangular slot 5 is broached or otherwise machined within thelower portion of brush holder insert 4, while the upper portion of brushholder insert 4 has an axial counterbore communicating with the axialrectangular slot 5 and being provided with suitable internal threads 6.

The axial rectangular slot 5 is adapted to snugly and slidably housebrush 7, which is a rectangular block of carbon or other suitablyconducting material. Brush 7 has a cylindrical collar 8integrally-fashioned thereon; and the lower portion of helical, coiledspring 9 seats upon collar 8 and extends longitudinally therefrom. Theopposite end of spring 9 seats upon an annular shoulder on conductingslug 10. A twisted, stranded copper wire is secured to collar 8 of brush7 and extends therefrom within spring 9 to be secured at its oppositeend to conducting slug 16, thus forming a suitable shunt 11 thatprovides a low-resistance electrical path to brush 7. Brush 7, collar 8,spring 9, slug 10, and shunt 11 thus comprise the brush, spring, andshunt subassembly 12.

A brush cap 13, made or brass or other suitably conducting material, hasa generally cylindrical surface on which external threads 14 arefashioned so as to mate with the internal threads 6 in brush holderinsert 4. Brush cap 13 has a blind axial bore 15 (shown moreparticularly in FIGURE 3), which is adapted to house and fully-guidespring 9. Slug 10 seats upon and makes finm electrical contact with theclosed end 16 of blind axial bore 15, as shown in FIGURE 3. Brush cap 13is seated and engaged within brush holder insert 4 and is securelylocked therein by means of an intervening cone lock washer 17. A flangedslotted head 18 is provided to enable brush cap 13 to become easilyengaged with brush holder insert 4; and when so engaged, the flangedslotted head 18 of brush cap 13 is recessed below the top of theenlarged upper portion of outer sleeve 1, thus allowing sufilcient roomfor insulated cap 19 to become seated within the enlarged upper portionof aesspoe 3 outer sleeve 1. It will be appreciated from an examinationof the drawings, particularly FIGURE 3, that the counter-boredinternally-threaded portion 2 of outer sleeve 1 constitutes an internalannular shoulder, that the counterbored internally-threaded portion 6 ofinner sleeve 4 has an outwardly-projecting annular flange seated uponthe internal annular shoulder, and finally, that the conducting brushcap 13 has an outwardly-projecting annular flange seating upon theannular flange of the inner sleeve, thus aiiording not only goodelectrical contact, but also, an additional mechanical support by meansof the cone lock washer 17 disposed therebetween. Insulated cap 19 issuitably slotted and provided with external threads to allow it to bereadily seated and engaged within the internally-threaded enlarged upperportion of outer sleeve 1.

As shown in FIGURE 3, outer sleeve It (when assembled to brush holderinsert 4, brush, spring, and shunt subassernbly 12, cone lock washer 17,brush cap 13, and insulated cap 1'9) is lightly press-fitted withincasing 20 of motor 21; and a roll-pin 22 made of. spring steel or othersuitable material is lodged within the transverse notch 23 so as to lockouter sleeve 1 against casing 20. Smooth-surfaced transverse roll-pin 22is more desirable than a locking screw or bolt having external threads.Otherwise, the inherent vibrations (however minute) would cause theexternal threads of the screw or bolt to cut and dig into and scrapeagainst the fibre surface of outer sleeve 1; and thus, within arelatively short period of time, such a locking means would beineffectual to hold outer sleeve 1 within casing 20'. As shown in FIGURE3, outer sleeve 1 is directed radially inward in such a manner wherebythe lower edge of protruding brush 7 makes sliding contact with commutator 24 of motor 21, with sufiicient pressure being exerted on brush7 by means of spring 9.

As shown in FIGURES 1 and 3, electrical connection to brush 7 is made bymeans of a conventional brush lead terminal spring 25, which comprises ahelical coiled spring folded back upon itself so as to form a circular,flexible terminal conductor capable of being enlarged and snapped overthe protruding bottom portion of brush holder insert 4. An annularrecess 26 is formed on brushholder insert 4 so as to accommodate brushlead terminal spring 25. When brush lead terminal spring 25 is foldedback upon itself (as shown in FIGURE 1) two extended portions thereofmesh within each other at 27, and the end of an electrical connector isinserted therein and soldered in place to hold brush lead terminalspring 25 together and keep the extended portions 27 from separating.The electrical connection is thus made from electrical connector 23 tobrush lead terminal spring 25 and via brush holder insert 4, brush cap13, conducting slug 10, and shunt 11 to brush 7. A hard fibre washer 29is predisposed between the end of outer sleeve 1 and brush lead terminalspring 25 to prevent any dirt or conducting foreign substances fromproviding an electrical path from brush spring terminal spring 25 tocasing 20.

Finally, a continuous steel band 30 is placed around the casing of motor21 and is positioned over cap 19 as shown in FIGURES 2 and 3, Band 291is secured to casing 20 by means of four screws 31, each being providedwith suitable lock washers 32; and band 29 thus provides an additionalmeans of maintaining the brushes within casing 20, i i i A v Torecapitulate briefly on some of the advantageous features of the presentinvention, spring 9 is fully-guided (not merely partially guided) withinblind axial bore 15 of brush cap 13 so that it cannot buckle and cannotfail to provide the necessary continuous pressure on brush 7. Brush cap13 is locked to brush holder insert by means of cone lock Washer 17. Anadditional cap 19 (made of hard fibre insulation) is secured withinouter sleeve 1. A smooth-surfaced transverse spring-steel rollpin 22(not an externally threaded screw) prevents outer sleeve 1 from becomingdislodged from casing 20. Finally, should the previous components becomeloose and disengaged from each other, steel band will prevent theoverall assembly, or any of the components thereof, from flying out ofcasing 26. The result is a muchneeded shockproof brush holder assemblyfully-capable of rendering at least 500 hours of trouble-free service(rather than merely 50 hours) under extreme conditions of shock andvibration, such as those encountered in a portable electric hammer.

Obviously, minor modifications and improvements may be made withoutdeparting from the basic spirit of the present invention. Therefore, itis to be understood that within the scope of the appended claims, theinvention may be practiced other than as specifically described.

I claim:

1. A shockproof brush holder assembly for an electric motor having amotor casing, comprising, an outer insulated sleeve including aninternally-threaded counterbored upper portion having an internalannular shoulder, an inner conducting sleeve firmly press-fitted withinsaid outer sleeve and having a lower portion protruding below said outersleeve, said inner sleeve including an internally threaded counterboredupper portion having an outwardly-projecting annular flange seated uponsaid internal annular shoulder of said inner sleeve, anexternallythreaded conducting cap seated within said counterboredportion of said inner sleeve, said conducting cap having a blind axialbore and further having an outwardly-projecting annular flange seatedupon said annular flange of said inner sleeve, whereby a brush, spring,and shunt subassembly may be housed within said bore of said cap andsaid inner sleeve, and an externally-threaded insulated cap seatedwithin said counterbored portion of said outer sleeve.

2. A shockproof brush holder assembly according to claim 1, whereinmeans, including an outer continuous band secured to the motor casingdirectly above he brush holder assembly, are provided to preclude thebrush holder assembly from movement outwardly of the motor casing. I I lReferences fired in the file of this patent

